Sighting means for target data acquisition are well known per se. These optical instruments are used by geodesists and by artillerists for example. Such equipment is comparable to a theodolite or transit compass, with a turntable for pointing a telescope toward a target. Typically, a compass, a computer with a CPU for running computer programs, an I/O unit, a memory, and a display device, or simply display, are included. Tilt and yaw angles from an observation site to a target are measured with a vernier. Most often, an active range-measuring device, such as an LRF, is also included.
It is taken for granted that modern sighting devices all include an optical device, e.g. a telescope or binoculars, and have to be powered-up and leveled before use. Optics, power-on, and leveling are standard and common practice in the art, and will therefore not be mentioned in the description below.
Also known in the art is the acronym DTM (digital terrain model), or DEM (digital elevation model) referring to a digitized topographic model, which provides a representation of a portion of terrain surface contour in the form of a three-dimensional digital map. Parties performing surface or volumetric calculations with respect to the modeled terrain, possibly make use of such a DTM. When the DTM is stored in a computer memory, it can be used as a unit in a terrain database. The stored DTM then provides the basic data for running surface and volumetric calculations implemented by a computer program associated with a computer and a computer memory. Various engineering, military and environmental related applications frequently refer to DTMs for surface or spatial calculations. A graphic illustration of a DTM is given in FIG. 1, to which reference is now made.
FIG. 1 shows a DTM surface S derived from a DTM database, associated with an (x,y,z) Cartesian-coordinate system, having a plane of grid points with (x,y) coordinates in the x-y plane. A (z) height-coordinate is defined for each discrete couple of (x,y) coordinates. Each point sampled on the terrain surface contour is represented by a junction of X and of Y lines in the grid. The height of each sampled point is given by values along the Z axis. The resolution of the sampling points of the DTM in the X–Y plane, and the accuracy of the height measurement of each sampled point depend on several factors, for example, on the quality of aerial photography from which the map was prepared.
In U.S. Pat. No. 5,086,396, Waruszewsky Jr. discloses “an aircraft navigation system” including “an inertial navigation system, a map of the terrain with elevation information stored in a digitized format as function of location, a typical energy managed of narrow (radar or laser) beam altimeter, a display system, and a central processing unit for processing data according to preselected programs. “This is an example of the use of a DTM for navigational purposes. Waruszewsky Jr. further points out that “The correct position of the aircraft with respect to the digitized map can permit the aircraft to engage in terrain following procedures using only the difficult to detect altitude range finding apparatus as a source of emitted electromagnetic radiation.” Hereby, Waruszewsky Jr. hereby refers to the problems associated with the detection of active sensors.
In U.S. Pat. No. 6,222,464, Tinkel et al. divulge “A method of automated scan compensation in a target acquisition system for reducing areas of potential threat surrounding an aircraft. The target acquisition system includes a scanning device with adjustable scan limits for scanning a desired area in the vicinity of the aircraft. “In their invention, Tinkel et al. make use of adjustable scanning limits to define a scanned area. In the published US Patent Application No. 20020180636 Al, Lin, Chian-Fang, et al. teach a passive ranging/tracking processing method that provides information from passive sensors and associated tracking control devices and GPS/IMU integrated navigation system, so as to produce three dimensional position and velocity information of a target. The passive ranging/tracking processing method includes the procedure of producing two or more sets of rection measurements of a target with respect to a carrier, such as sets of elevation and azimuth angles, from two or more synchronized sets pf passive sensors and associated tracking control devices, installed on different locations of the carrier, computing the range vector measurement of the target with respect to the carrier using the two or more sets of direction measurements, and filtering the range vector measurement to estimate the three-dimensional position and velocity information of the target. Use is made of passive sensors, but there are needed two or more synchronized sets of passive sensors.